1. Field of the Invention
This invention relates to methods and apparatus for heating metal or other material by high-temperature gas in a furnace, and particularly relates to heating methods and apparatus whereby heat energy contained in high-temperature gas used for heating a material is recovered when the gas is discharged.
2. Description of the Prior Art
In the prior art, when heat is to be recovered from gas used for heating a material and discharged from the heating furnace, the gas discharged from the furnace is introduced through a flue into a recuperator located separate from the furnace. Some of the prior inventors, however, have proposed that a heat exchanger be located along the inner surface of a heating furnace instead of a recuperator being disposed separate from the furnace, because by so doing the heat recovery from exhaust gas may be made with no equipment provided outside the furnace and no additional cost therefor and with no heat loss of the exhaust gas flowing through the flue connecting the furnace to the external recuperator. However, such a proposal is not a satisfactory solution because the heat exchanger disposed inside the furnace absorbs heat, lowering the temperature in the furnace so that inadequate heating of the material may result.